Blowing agent compositions

ABSTRACT

A blowing agent composition is provided comprising an azodicarbonamid; zinc oxide, zinc carbonate or a zinc salt of C 1  -C 4  organic acid; and an aromatic sulfinic acid or a metal salt of an aromatic sulfinic acid. For each hundred parts by weight of the azodicarbonamid, the zinc oxide, zinc carbonate or zinc salt is 0.25-25 parts by weight and the aromatic sulfinic acid or metal salt is from 1-2000 parts by weight for each 100 parts of the zinc oxide, zinc carbonate or zinc salt. The total weight of the zinc oxide, zinc carbonate or zinc salt plus the aromatic sulfinic acid or metal salt is from 20-25 parts by weight.

This is a division of application Ser. No. 399,518, filed July 19, 1982.

The present invention relates to improved blowing agent compositions,and their preparation and use.

When making an expanded material such as a foamed, synthetic polymericmaterial, the polymeric material has conventionally been mixed with ablowing agent, such as azodicarbonamide. The performance requirements ofblowing agents have now become more and more critical and changes in thecomposition of the blowing agents can have significant effects on theend product.

Various azodicarbonamide blowing agents are known in the prior art forblowing gas-expandable polymeric material. U.S. Pat. No. 3,903,015discloses a combination of azodicarbonamide and a sulfinic acid or salt.U.S. Pat. No. 4,312,776 discloses a blowing agent composition comprisinga combination of azodicarbonamide, a chromium sulfate and a zinccompound. Similarly, British Pat. No. 1,581,252 discloses an olefinpolymer, a cross-linking agent having a decomposition temperature belowthat of azodicarbonamide and a chromium compound. U.S. Pat. No.4,263,165 discloses a blowing agent composition comprisingazodicarbonamide, zinc oxide and benzenethiol sulphonic acids.

Disadvantages with the known azodicarbonamide blowing agents include theproduction of non-uniform cells, yellow color appearing in the expandedmaterial, a density of the expanded material being higher than might bedesired and insufficient release of gas at low reaction temperatures.

As will be shown below, the instant invention overcomes many problemsfaced in the prior art blowing agents. The blowing agent of theinvention results in improved control of reduction of decompositiontemperature, rate of decomposition and the amount of gas released in theblowing process. The present invention also results in the production ofan expanded polymeric material having an improved cell structure,improved uniformity of cells and reduction of discoloration.

It should be noted that the present invention is useful in bothnon-cured and cured systems and is especially useful when curing orcross-linking of a polymer is desired because it is critical to controlthe rate of expansion with rate of degree of cure. For example, somepreliminary cure is beneficial before decomposition of the blowing agentoccurs. The rubber or plastic desirably has some firmness to prevent gasfrom escaping yet should not be too highly cured otherwise cells cannotform properly. Eventually, when full expansion is achieved, the rubberor plastic should be fully cured.

An important aspect of the invention is that it may provide expansion at125° C. or lower, but preferably below 145° C., and generally can beused below 160° C.

In accordance with the invention, a blowing agent composition isprovided comprising: (a) 100 parts azodicarbonamide; (b) 0.25-25 partszinc oxide, zinc carbonate or a zinc salt of C₁ -C₄ organic acid; and(c) for every 100 parts of (b) from 1-2000 parts aromatic sulfinic acidor metal salt of aromatic sulfinic acid, wherein the ratio of (a) to(b+c) is in the range of 100/2 to 100/25, all by weight.

In accordance with the invention for expansion of rubber, one may useabout 16-30 parts of blowing agent composition to achieve about 0.1g/cm³ or less, 12-15 parts for about 0.15 g/cm³ and about 4-10 parts forabout 0.5 g/cm³ density all per 100 parts of rubber.

It should be understood, however that these requirements may varydepending on the original density of the rubber compound used.

For the expansion of plastics such as polyethylene, usually 0.5 to 30parts of the blowing agent composition may be employed leading todensity reductions of 50 to over 96%.

Preferred thermoplastic polymeric materials include natural andsynthetic resins (for example acrylonitrile-butadiene rubbers and blendsof acrylonitrile-butadiene rubbers with polyvinyl chloride), polyvinylchloride, polyvinylidene chloride, polyvinylacetate, polyethylvinylacetate, polyesters (for example polyethylene terephthalate, andpolybutylene terephthalate), polyolefins (for example low and highdensity polyethylene, and polypropylene), modified polyphenylene oxides,polystyrenes, natural and synthetic rubbers (for exampleethylene-propylene rubber, nitrile rubbers, polyisoprene rubber),copolymers of the monomers amongst themselves or with other monomers,(for example a copolymer of ethylvinyl acetate and olefin (such asethylene or propylene) and mixtures thereof.

Particularly preferred thermoplastics polymeric materials includepolyolefins (for example, low and high density polyethylene andpolypropylene) and olefin copolymers (for example, copolymers ofethylene and ethylvinyl acetate), preferably those which may becross-linked before expansion, for example, by means of chemicalcross-linking agents or by ionising radiation.

Suitable aromatic sulfinic acids or salts include: benzene sulfinicacid; sodium benzene sulfinate; magnesium-di(benzene sulfinate);ammonium benzene sulfinate; trimethylammonium benzene sulfinate;tertiary butyl ammonium benzene sulfinate; cyclohexyl ammonium benzenesulfinate; benzyl ammonium benzene sulfinate; p-toluene sulfinic acid;barium bis-(p-toluene sulfinate); zinc bis-(p-toluene sulfinate);di-sec.-butylammonium p-toluene sulfinate; morpholinium-p-toluenesulfinate; piperazinium-p-toluenesulfinate; magnesiumbis-(p-chlorobenzene sulfinate); zinc bis-(p-chlorobenzene sulfinate);2,4-dimethylbenzene sulfinic acid; potassium 2,4-dimethylbenzenesulfinate; barium bis-(2,4-dimethylbenzene sulfinate);lead-bis.-(2,4-dimethylbenzene sulfinate); sodium 2,5-dimethylbenzenesulfinate; zinc bis-(2,5-dimethylbenzene sulfinate);2-chloro-4-methyl-benzene sulfinic acid; sodium p-bromobenzenesulfinate; and p-tertiary butyl-benzene sulfinic acid.

Suitable zinc compounds are zinc oxide, zinc carbonate, zinc diformate,zinc diacetate, zinc dipropionate and zinc dibutyrate.

The composition may also include a peroxide promoter. As peroxidepromoters, chromium sulfates, especially basic chromium sulfates areemployed having the approximate general formula Cr₂ (SO₄)₃.6H₂ O or Cr₂(SO₄)₃.15H₂ O, or potassium chromium sulfate of the approximate formulaKCr(SO₄)₂.12H₂ O. Also suitable are sodium chromates (Na₂ CrO₄ ; Na₂CrO₄.10H₂ O) and chromium phosphates (CrPO₄.2H₂ O; CrPO₄.6H₂ O). Thepreferred peroxide promoter is trimethylolpropane trimethylacrylatewhich may be used alone or in combination with the other promoters.

In many instances the addition of a nucleating agent is also desired. Itis preferred to use decabromodiphenyl ether, but also silicates, chalk,silica, and like compounds may be used.

It is important that the azodicarbonamide, the zinc compounds and thearomatic sulfinic acid (salt) be premixed before adding them to thefoamable rubber or plastic. For convenience and improved effectivenessthe peroxide promoters and nucleating agents may also be pre-blendedwith the above three ingredients. Curatives for rubber and plastics arewell known in the art. Usually, rubbers are crosslinked by means ofsulfur type curing systems including accelerators, retarders and thelike. Peroxides are employed for the purpose of crosslinking rubbers andplastics. Care must be taken that the curative activation temperaturefalls within the decomposition temperature range of the blowing agentcomposition; preferably, the onset of curing should occur somewhat belowsuch decomposition temperature.

The following examples, in which all parts and percentages are onlyweights unless otherwise noted, are given to illustrate the invention.

    ______________________________________                                        Ingredients used:                                                             ______________________________________                                        EPDM:       Ethylene (52%)-propylene (39%)-5-ethyli-                                      dene-2-norbornene (9% by weight) ter-                                         polymer; ML-4 at 125° C.: 68.                              SBR:        Blend of 80 parts SBR (5% styrene) and 20                                     parts SBR (85% styrene): ML-4 at 100° C.:                              25.                                                               ClBR:       Polychloroprene; ML-4 at 100° C.: 50.                      Clay:       Specific gravity 2.6; particle size: ca.                                      95% less than 2 micron (SupreClay                                             [trademark]).                                                     Petrolatum: Petroleum hydrocarbon.                                            Extender oil:                                                                             Naphthenic oil; SUS at 38° C. (Circosol                                [trademark] 4240).                                                Paraffin wax:                                                                             m.p. 60-65° C. (Sunproof [trademark]                                   Improved Wax).                                                    Antioxidant:                                                                              Reaction product of diphenylamine and                                         secondary amine (Octamine [trademark]).                           MBTS:       Mercaptobenzothiazole, curative.                                  DPG:        Diphenylquanidine.                                                PE:         Polyethylene; density 0.92 g/cm.sup.3.                            ADC-1:      Azodicarbonamide; av. particle size: 3                                        micron (average) (Celogen [trademark] AZ                                      130).                                                             ADZ-2:      As above; particle size 9-12 micron.                              ZnO:        Zinc oxide.                                                       ZnAc:       Zinc diacetate.                                                   ZnCO.sub.3 :                                                                              Zinc carbonate.                                                   ZPTS:       Zinc di(p-toluenesulfinate).                                      PPR-1:      Peroxide promoter No. 1: trimethylolpro-                                      pane trimethacrylate.                                             PPR-2:      Perioxide promoter No. 2: basic chromium                                      sulfate.                                                          PPR-3:      Sodium chromate.                                                  PPR-4:      Chromium phosphate.                                               NA-1:       Nucleating agent No. 1: decarbromodi-                                         phenyl ether.                                                     NA-2:       Nucleating agent No. 2: calcium silicate.                         NA-3:       Nucleating agent No. 3: hydrous alumina                                       silicate.                                                         ______________________________________                                    

EXAMPLE 1 Determination of Gas Evolution

Several blowing agent compositions were prepared by thoroughly mixingthe various ingredients indicated in Table I in a Waring [trademark]blender. To ca. 1 g of composition, about 25 ml of dioctyl phthalate isadded and the total mixture is mulled until a uniform mixture isobtained. A carefully weighed sample (ca. 5 g) is taken and placed in agas evolution measuring device preheated to a set temperature.

Gas evolutions are determined at various times thereafter as summarizedin Table 1.

                  TABLE 1                                                         ______________________________________                                        Run No.   1      2      3    4    5    6    7*  8*                            ______________________________________                                        ADC, parts                                                                               90     90     90   90   90   90  90  90                            ZnO, parts                                                                               10     10     10   10   10   10  10  --                            ZPTS, parts                                                                              1      2      3    4    5    10  --  10                            Gas evolution development at 135° C., cm.sup.3 /g of composition       Minutes                                                                       1:         4      6      5    4    7    4        4                            3:         4      7      7    5    9    8        6                            5:         5      9      9    8    12   17      14                            7.5:       7      11     15   18   22   53      22                            10:        12     22     33   47   50    93     26                            15:        53     78     96   98  102  112      31                            20:        89    102    115  111  116  121      34                            25:       110    115    124  120  125  125      38                            30:       127    122    132  127  130  128   0  40                            30 Minutes Gas Evolution, adjusted to 1 g ADC                                 cm.sup.3 /g                                                                             143    138    151  147  152  156   0  44                            ______________________________________                                         Remarks:                                                                      *Prior art compositions for comparison to the invention.                 

The data indicate not only that gas evolution in Runs No. 1-6 isunexpectedly remarkably increased over known compositions, Runs No. 7and 8, but also that with increasing levels of ZPTS the rate of gasevolution is accelerated.

EXAMPLE 2

Using the procedure of Example 1, additional total gas evolutions at135° C. were determined on compositions containing varyingconcentrations of zinc oxide and ZPTS. The results are indicated inTable II.

                  TABLE II                                                        ______________________________________                                        Run No.        9     10        11   12                                        ______________________________________                                        ADC, parts    90     10        90   90                                        ZnO, parts     5      7        14   21                                        ZPTS, parts    5      3         6    7                                        Results                                                                       cm.sup.3 /g, actual                                                                         84     115       106  111                                       cm.sup.3 /g, adjusted*                                                                      93     128       129  136                                       ______________________________________                                         *calculated to cm.sup.3 /one gram ADC                                         Remarks:                                                                      Increasing the concentration of ZnO leads to increasing amounts of            adjusted gas evolved.                                                    

EXAMPLE 3

Further gas evolution measurements were undertaken to determine theeffect of various lower levels of the aromatic sulfinic acid salt. Thesame procedure as in Example 1 was adopted. The various compositions andgas evolution developments at 135° C. and 149° C. are listed in TableIII. Runs No. 21 and 22 are prior art compositions made for comparisonto the invention.

                                      TABLE III                                   __________________________________________________________________________    Run No.                                                                              13  14  15  16  17  18  19  20  21  22  23  24                         __________________________________________________________________________    ADC, parts                                                                           90  90  90  90  90  90  90  90  90  90  90  90                         ZnO, parts                                                                           5   10  10  10  10  10  20  10  10  --  --  --                         ZnCO.sub.3, parts                                                                    --  --  --  --  --  --  --  --  --  --  10  --                         ZnAC, parts                                                                          --  --  --  --  --  --  --  --  --  --  --  10                         APTS, parts                                                                          0.5 0.1 0.25                                                                              0.5 0.75                                                                              1.0 0.5 10  --  10  1.0 1.0                        Gas evolution at 135° C., cm.sup.3 /g                                  Time                                                                          (Minutes)                                                                     1:     5   5   4   5    6   5   4   4  --   4   9   7                         3:     5   6   5   6    7   7   4   8  --   6   9  14                         5:     5   6   5   6    7   7   5  17  --  14  11  25                         7.5:   6   6   5   6    7   7   6  53  --  22  14  39                         10:    7   6   5   7   10   9   6  93  --  26  24  47                         15:    8   6   5   10  21  20  13  112 --  31  72  59                         20:    15  6   5   21  50  59  54  121 --  34  117 70                         25:    31  7   8   58  80  86  142 125 --  38  140 76                         30:    49  9   15  108 103 106 147 128  0  40  --  --                         30 Minute Gas Evolution at 135° C., adjusted to 1 g ADC                cm.sup.3 /g                                                                          52  10  17  126 115 119 180 156  0  44  157 82                         Gas evoluation at 149° C., cm.sup.3 /g                                 Time                                                                          (minutes)                                                                     1:     4   5   4   4    6   4  --  --  --  --   7   9                         3:     5   6   5   6    9   5  --  --  --  --  11  21                         5:     9   7   6   9   11  10  --  --  --  --  35  46                         7.5:   28  13  16  64  125 126 --  --  --  --  172 105                        10:    73  110 161 163 165 162 --  --  --  --  175 149                        15:    156 168 164 167 165 164 --  --  --  --  178 166                        20:    172 --  --  --  --  --  --  --   0  112 178 180                        Ultimate Gas evolution at 149° C., adjusted to 1 g ADC                 cm.sup.3 /g                                                                          183 187 183 186 185 184 --  --   0  124 200 202                        __________________________________________________________________________

The results indicate that even at low ZPTS concentrations, satisfactorygas evolutions can be achieved at 135° C., and even those compositionswhere the gas evolutions were less than desired at that temperature(Nos. 13, 14 and 15), their ability to provide controlled release of gasat copious amount is demonstrated by the 149° C. tests. Run No. 23 (Na₂CO₃) performed most satisfactorily and Run No. 24 (zinc diacetate)performed very well at 149° C.

The usefulness of the blowing agent compositions of this invention wasinvestigated for the expansion of rubbers and plastics as follows:

EXAMPLE 4

Two rubber masterbatches were prepared using the following recipes:

    ______________________________________                                        Masterbatch, parts by weight                                                  ______________________________________                                        EPDM             30                                                           SBR              75                                                           ClBR             10                                                           Stearic acid      4                                                           Clay             100                                                          Silica filler    50                                                           N550 FEF, Black  10                                                           Petrolatum       10                                                           Extender oil     45                                                           Paraffin Wax      5                                                           Antioxidant       1                                                           Total            340                                                          ______________________________________                                    

On a Banbury [trademark] type B laboratory internal mixer all theingredients were blended at a No. 2 speed while cooling. After 1.5minutes, the ram was raised and scraped, and blending was continued forabout another 3.5 minutes, then the batch was removed (batch temperatureca. 125° C.).

Two rubber stocks were then compounded on a two-roll mill using theseingredients

                  TABLE IV                                                        ______________________________________                                        (all in parts by weight)                                                      Run No.          24      25.sup.(1)                                           ______________________________________                                        Masterbatch      340.0   340                                                  MBT              0.75    0.75                                                 DPG              0.45    0.45                                                 Sulfur           2.75    2.75                                                 BAC.sup.(2)      13.0    --                                                   ADC-1            --      11.58                                                ZnO              --      1.29                                                 ZPTS             --      0.13                                                 Total parts      356.95  356.95                                               ______________________________________                                         Remarks:                                                                      .sup.(1) Prior Art, for comparison to invention.                              .sup.(2) Preblend of ADC1 (100 parts), ZnO (11 parts) and ZPTS (1.1           parts).                                                                  

From each compounded stock blanks were formed (dimensions: 9.52×9.52×1.9cm) weighing 300 g each by placing them in molds. The molds containingthe slabs were placed in a press and were precured therein for 48minutes at 143° C. Upon removing the precured slabs, they expandedrapidly to about 150% of their original size. Further expansion and curewas accomplished by keeping the two slabs in an oven for 1.5 hours at154° C., after which time they were taken out of the oven and cooled.

Physical characteristics were determined the following day with theseresults:

    ______________________________________                                        Run No.         24'      25'                                                  ______________________________________                                        Density         0.17     0.22                                                 Surface         smooth   large blisters                                       Cell structure  fine     fine - very coarse                                   Cell uniformity excellent                                                                              very bad                                             Compression set, %                                                                            46       75                                                   (ASTM D-1056)                                                                 ______________________________________                                    

The expanded and cured slab of this invention (No. 24') excelled by itsfine uniform cell structure and overall smooth appearance, whereas No.25' contained large blisters on the surface and a most irregular corehaving large cavities. It is quite apparent that with regard to densityand compression set, Run No. 24' is an unexpectedly superior product.

EXAMPLE 5

The blowing agent composition of this invention was evaluated for theexpansion of polyethylene while simultaneously curing. A basic recipewas used throughout (all in parts by weight), namely:

    ______________________________________                                        Polyethylene      84                                                          BAM*              15                                                          Dicumylperoxide**  1                                                          ______________________________________                                         *blowing agent composition or mixture                                         **Di Cup [trademark] R                                                   

The test samples were prepared in the following manner:

The polyethylene granules were placed on a two-roll mill heated to abovetheir crystalline melting point and milled until the polymer melted orfluxed. Then, the BAM mixture (for details, see Tables V-VIII) was addedas well as the peroxide and milling was continued for 5 minutes at thattemperature. The compounded polyethylene was then sheeted off the milland a circle (diameter: 12.7 cm) is cut from the center of the sheet.This circle is then placed in a press and heated at 121° C. for twominutes for shaping. From the center of this circle is cut a smallercircular piece having a 7.62 diameter. The latter is exposed to 204° C.temperature in an air circulating oven until optimum expansion isachieved.

In Tables V-VIII, only the ingredients comprising the blowing agentmixture are listed. Prior to the addition to the polyethylene, theseingredients are thoroughly mixed in a Waring [trademark] blender.

The cured and expanded polyethylene samples, after cooling, were cut toorder to examine cell structure and cell uniformity. Densitymeasurements were undertaken as well as the color of the samples wasobserved. The following ratings were applied to the resultant samples(note the abbreviations used in the Tables):

    ______________________________________                                        Criterion      Result       Rating                                            ______________________________________                                        Density, cm.sup.3 /g:                                                                        greater than 0.07                                                                          0                                                                0.063-0.07 1                                                                  0.056-0.062  2                                                                0.048-0.055  3                                                                 0.04-0.047  4                                                                less than 0.04                                                                             5                                                 Cell structure:                                                                              vc (very coarse)                                                                           1                                                                c (coarse)   2                                                                m (medium)   3                                                                f (fine)     4                                                                vf (very fine)                                                                             5                                                 Cell uniformity:                                                                             n-u (non-uniform)                                                                          1                                                                u (uniform)  5                                                 Color:         vy (very yellow)                                                                           1                                                                y (yellow)   2                                                                ly (light yellow)                                                                          3                                                 ______________________________________                                    

Ratings of 9 and higher are desirable, preferably 11 or higher and mostpreferably 13 or higher.

In Runs No. 26-31, the blowing agent composition was employed alone aswell as with certain peroxide promoters and nucleating agents. Runs No.32-36 are prior art made for the purposes of comparison. For details seeTable V.

                                      TABLE V                                     __________________________________________________________________________    Run No. 26  27  28  29  30  31  32* 33* 34* 35* 36*                           __________________________________________________________________________    ADC     100 100 100 100 100 100 100 100 100 100 100                           ZnO     4.8 9.6 5.  11. 0.4 0.4 0.4 --  0.4 0.4 0.4                           ZPTS    0.5 1.0 0.5 1.1 2.7 2.7 --  4.5 --  --  --                            PPR-1   --  --  3.8 4.0 3.8 3.8 3.8 3.8 3.8 3.8 3.8                           PPR-2   --  --  --  --  --  0.5 --  --  0.5 --  --                            NA-1    --  --  --  --  --  0.3 --  --  --  0.3 --                            NA-2    --  --  --  --  --  1.1 --  --  --  --  1.1                           NA, total                                                                             --  --  --  --  --  1.4 --  --  --  0.3 1.1                           Results                                                                       D, (g/cm.sup.3)                                                                         0.05                                                                             0.04                                                                              0.034                                                                             0.027                                                                             0.042                                                                             0.037                                                                             0.094                                                                             0.045                                                                             0.074                                                                             0.072                                                                             0.11                         Cell structure                                                                        c   c   c   c   c   f   c   vc  c   m   c                             Color   ly  ly  ly  ly  ly  ly  vy  y   y   y   vy                            Cell uniformity                                                                       u   u   u   u   u   u   n-u n-u n-u n-u n-u                           Rating   11  12  13  13  12  15  4   8   5   6   4                            __________________________________________________________________________     *prior art, made for the purpose of comparison with the invention.       

It is quite apparent from the results that the expanded polyethyleneusing the blowing agent composition of this invention consistently hasspecific and especially overall properties better than the experimentsusing known methods.

EXAMPLE 6

In order to determine the effect of nucleating agent when expandingpolyethylene, additional experiments were conducted. The procedure ofExample 5 was essentially employed. Table VI summarizes the results ofRuns No. 37-41.

                  TABLE VI                                                        ______________________________________                                        Run No.     37      38      39    40    41                                    ______________________________________                                        ADC-2       100     100     100   100   100                                   ZnO         0.4     0.4     0.4   0.4   0.4                                   ZPTS        3.8     2.7     2.7   2.7   3.9                                   PPR-1       3.8     3.8     3.8   3.8   3.9                                   PPR-2       0.5     0.5     0.5   0.5   0.6                                   NA-1        --      --      0.3   0.3   3.3                                   NA-2        --      1.1     --    0.5   1.1                                   NA-3        --      --      1.1   --    --                                    NA, total   --      1.1     1.1   0.8   4.4                                   Results                                                                       D, g/cm.sup.3                                                                              0.042   0.046   0.041                                                                               0.043                                                                               0.046                                Cell structure                                                                            m       f       c     f     m                                     Color       y       ly      ly    ly    ly                                    Cell uniformity                                                                           Uniform throughout                                                Rating       12      14      12    14    13                                   ______________________________________                                    

The addition of a nucleating agent appears beneficial for reduction ofcolor, but they are not essential for the preparation of a foam.Decabromodiphenyl ether and calcium silicate seem somewhat moreeffective then hydrous alumina silicate.

EXAMPLE 7

Various concentrations and ratios of ingredients, i.e., within theblowing agent composition per se, the peroxide promoters and nucleatingagents were used in the preparation of expanded and cured polyethylene.The same procedure as in Example 5 was used; details and results arepresented in Table VII.

                                      TABLE VII                                   __________________________________________________________________________    Run No.                                                                              42  43  44  45  46  47  48  49                                         __________________________________________________________________________    ADC-2  100 100 100 100 100 100 100 100                                        ZnO    0.3 0.7 2.3 0.4 0.5 0.5 0.4 0.4                                        ZPTS   2.7 1.6 0.3 3.9 8.0 2.9 2.7 2.7                                        PPR-1  3.8 3.8 3.8 1.7 4.0 11.7                                                                              3.8 3.8                                        PPR-2  0.5 0.5 0.5 0.6 0.6 0.6 0.3 0.8                                        NA-1   0.3 0.3 0.3 0.3 0.3 0.3 0.3 0.3                                        NA-2   1.1 1.1 1.1 1.1 1.1 1.2 1.1 1.1                                        NA: total                                                                            1.4 1.4 1.4 1.4 1.4 1.5 1.4 1.4                                        Results                                                                       D: (g/cm.sup.3)                                                                       0.05                                                                              0.056                                                                             0.035                                                                             0.07                                                                              0.04                                                                              0.046                                                                             0.04                                                                              0.035                                     Cell structure                                                                       f   f   m   m   c   c   m   vf                                         Color  y   y   ly  y   y   vy  y   y                                          Rating  12  11  14  9   11  10  11  13                                        __________________________________________________________________________

(All samples exhibited uniform cell structure).

The blowing agent composition of this invention in combination withperoxide promoters provide a range of ingredient ratios for making curedand expanded plastics.

EXAMPLE 8

The effectiveness of certain chromium type peroxide promoters wasinvestigated as well as the use of zinc carbonate as blowing agentenhancer for the purpose of expanding and crosslinking polyethylene. Themethod of Example 5 was substantially employed. Experimental details andresults are disclosed in Table VIII.

                  TABLE VIII                                                      ______________________________________                                        Run No.  50      51      52    53    54    55                                 ______________________________________                                        ADC-2    100     100     100   100   100   100                                ZnO      0.4     0.4     0.4   2.5   2.5   --                                 ZnCO.sub.3                                                                             --      --      --    --    --    0.4                                ZPTS     2.7     2.7     2.7   0.3   0.3   2.7                                PPR-1    3.8     3.8     3.8   3.8   3.8   3.8                                PPR-2    --      --      --    --    --    0.8                                PPR-3    --      0.4     --    0.4   0.8   --                                 PPR-4    --      --      0.5   --    --    --                                 NA-1     1.1     1.1     1.1   1.1   1.1   1.1                                Total NA 1.4     1.4     1.4   1.4   1.4   1.4                                D, g/cm.sup.3                                                                           0.046   0.04    0.09  0.035                                                                               0.035                                                                               0.05                              Cell structure                                                                         c       f       vf    f     f     c                                  Cell unifor-                                                                           u       u       u     u     n-u   u                                  mity                                                                          color    ly      ly      ly    ly    ly    y                                  Rating    12      14      11    15    13    10                                ______________________________________                                    

From the results, it is apparent that certain chromium compounds may beused for improving all structure and uniformity with good to excellentoverall ratings. The use of zinc carbonate instead of zinc oxideprovided a satisfactory product.

EXAMPLE 9

The usefulness of this invention was further tested on a compoundedrubber-plastic mixtures using the following recipes, all in parts byweight:

    ______________________________________                                        Run No.          56      57*                                                  ______________________________________                                        EPM.sup.(1)      30      30                                                   EVA.sup.(2)      70      70                                                   Filler.sup.(3)   30      30                                                   Zinc oxide       2       2.5                                                  Zinc stearate    2       2                                                    Peroxide.sup.(2) 6       6                                                    Extender oil.sup.(5)                                                                           15      15                                                   ADC-1            --      4.45                                                 ZPTS             --      0.05                                                 BAC.sup.(6)      5       --                                                   Stearic acid     1       1                                                    Total Parts      161     161                                                  ______________________________________                                         Remarks:                                                                      .sup.(1) Ethylene (45%) propylene (55%) copolymer; ML4 at 100° C.:     45                                                                            .sup.(2) Ethylene (72%)  vinyl acetate (28%) copolymer; Melt Index: 6         .sup.(3) Precipitated hydrated amorphous silica (Hi Sil [trademark] 233)      .sup.(4) Bis(tbutylperoxy) diisopropylbenzene (40% on Burgees clay; Vulcu     [trademark] 40KE)                                                             .sup.(5) Paraffinic oil (Sunpar [trademark] 2280)                             .sup.(6) (as in Example 4, Table IV)                                          *For the purpose of comparison with the invention.                       

The compounds were prepared as follows: EPM and EVA were mixed in aBanbury (type B) internal mixer for 2 minutes, then filler, zinc oxide,zinc stearate and extender oil were charged, the batch temperature beingabout 88° C. Blending was continued for about 4 minutes, and therespective remaining ingredients were added, and the batches wereremoved from the mixer after two more minutes of blending (temperatureca. 121° C.). The stocks were sheeted out on a two-roll mill (80°-90°C.) and (8.9×12.7 cm) pads were formed weighing about 170 g. These padswere placed in a (8.9×12.7×1 cm) mold and pressed at about 1500 psi(10.5 MPa) and cured under pressure for 38 minutes at 143° C.

When removing the pads, they expanded rapidly. Core samples were takenand the characteristics of the cooled (to room temperature) productsdetermined.

    ______________________________________                                        Run No.      56             57                                                ______________________________________                                        Density, g/cm.sup.3                                                                        0.17           0.20                                              Color        white          light yellow                                      Uniformity   uniform        nonuniform                                                     (minor irregularities)                                           Surface      smooth         blisters                                          Cell structure                                                                             fine-med.      fine-coarse                                       ______________________________________                                    

It was difficult to remove sample 57' from the mold due to stickiness(no problems were encountered with sample 56'). Generally, the runprepared according to this invention, namely the addition of preblendedblowing agent composition, exhibited density and cell characteristicsunexpectedly superior to those of the comparison example.

We claim:
 1. A masterbatched blowing agent composition for foaming apolymeric composition consisting essentially of:(a) azodicarbonamide;(b) zinc oxide, zinc carbonate or a zinc salt of C₁ -C₄ organic acid;and (c) an aromatic sulfinic acid or a metal salt of an aromaticsulfinic acid,wherein for each 100 parts by weight of (a), (b) is0.25-25 parts by weight and (c) is from 1-2000 parts by weight per 100parts of (b) and the total of (b)+(c) is from 2-25 parts by weight andsubstantially in the absence of the polymeric composition to be foamedfully comprising a trimethylolpropane trimethacrylate peroxide promoter.2. A composition comprising a gas expandable polymeric material and ablowing agent composition comprising:(a) azodicarbonamide; (b) zincoxide, zinc carbonate or a zinc salt of C₁ -C₄ organic acid; and (c) anaromatic sulfinic acid or a metal salt of an aromatic sulfinicacid,wherein for each 100 parts by weight of (a), (b) is 0.25-25 partsby weight and (c) is from 1-2000 parts by weight per 100 parts of (b)and the total of (b)+(c) is from 2-25 parts by weight and substantiallyin the absence of the polymeric composition to be foamed fullycomprising a trimethylolpropane trimethacrylate peroxide promoter.